But the move that stuck was Sagan’s — he jumped as the chase caught the escapees, Kwiatkowski quickly followed, and the two took a lead of more than 30 seconds onto the ninth of 10 gravel sections.

With 14km to go their advantage was more than a minute, and behind, Alejandro Valverde (Movistar) was frantically trying to get something going. He finally got away from the others, but not for long — Roman Kreuziger (Tinkoff-Saxo), Damiano Cunego (Lampre-Merida) and two-time winner Fabian Cancellara (Trek Factory Racing) rode up to him and it was a four-way battle for the final spot on the podium.

Inside the final kilometer the two leaders were secure, 43 seconds ahead of that four-man chase. Sagan was on the front as the road tilted up, but he wasn’t looking indomitable, with Kwiatkowski parked comfortably on his wheel.

Sagan made a show of ramping up the effort on the final ascent — but then the Polish champion exploded off his wheel and rocketed toward the line. Sagan had no response, and Kwiatkowski soloed in for the victory. Sagan followed 19 seconds later to take a second consecutive runner-up finish here; in 2013, he finished behind teammate Moreno Moser.

With the top two spots on the podium thus decided, Valverde once again left his companions behind to cross third at 36 seconds down.

“Winning in Siena here is an amazing feeling,” Kwiatkowski said. “I know Sagan has much more experience on a final like that in the big races. I was watching even the chainring he was using to make sure I didn’t make any stupid mistakes.”

On the final climb, Sagan slowed a bit, and Kwiatkowski said he knew the Cannondale rider was suffering.

“So I went full gas until the end and that’s how it was won,” he said. “When I came around the final corner to the finish line in Piazza del Campo, it was absolutely beautiful.”

As for Sagan, he said simply: “You win and you lose. It happened to me today. No, I have not had any mechanical problem — just in the end I had no legs.”

Valverde pronounced himself pleased with his finish in a race he called “wonderful, but still really hard, almost five hours and a half on the bike, even harder this year due to the wind.”

A moment’s indecision when Sagan and Kwiatkowski attacked made it more difficult still, he added.

“That moment of hesitation is crucial so many times, to not let them go,” Valverde said. “I followed Cancellara’s wheel and wasn’t really thinking they would open such a big gap.”